The conventional liquid containers mostly have only one opening for filling in or pouring out its content, and the liquid can hardly be poured out smoothly because of the imbalance of the pressures inside and outside the container. Even if it has two openings, two caps of the openings have to be taken down so as to make the flowing out of the liquid smooth, and it is very possible that the removed caps may be lost or contaminated. In order to improve the defect mentioned above, the applicant has devised this invention.